The invention relates to a rapidly extendable jack intended for use with boat trailers, camping trailers, farm equipment and the like. The jack can be rapidly advanced or retracted to a desired height and also possesses additional height capacity over ordinary jacks.
Various types of jacks are known and used throughout the country. A common example is a car jack which consists of a lift device connected to a height adjustment mechanism that is mounted on a standard, and the mechanism allows continuous cranking of the lift device up the standard. Another example is a trailer jack which typically consists of two telescoping pieces with a height adjustment means that extends or retracts one piece in relation to the second. Usually, this height adjustment means is a threaded bolt and nut. The nut is placed in the top end of the inner telescoping piece and the bolt is threadably engaged through the nut and extends inside the telescoping piece. The bolt also extends through the end of the outer piece where it is connected to a handle used to crank the jack. In use, the handle is extended from or retracted into the outer piece. A jack of this type is disclosed in U.S. Pat. No. 3,595,527.
The problem with this type of standard two-piece telescoping jack is that the jack must be cranked continuously from the fully retracted position to the desired extended position, i.e., the nut must be turned down the bolt. In use, the jack typically is extended 12 inches or more requiring 100 to 125 complete turns on the handle for the jack to be the desired height to contact the ground from the tongue of a trailer. Then an additional 20-25 cranks are necessary to further raise the trailer. This cranking must be repeated to retract the jack. This excessive cranking can cause wear and tear on the jack and on the person doing the cranking. Therefore, it would be very desirable to have a jack capable of rapid advance and retraction.
U.S. Pat. No. 3,595,527 discloses a jack assembly somewhat capable of rapid retraction and extension. It discloses the use of a standard two-piece telescoping jack that is inserted through a tubular support. The outer piece of the jack has radial projections along its side that engage within an L-shaped slot in the tubular support. The jack is simply adjusted in relation to the support. Other types of jacks somewhat capable of rapid advance are disclosed in U.S. Pat. Nos. 4,078,774; 4,221,362; 3,957,249; 3,709,467; and 2,529,292. The present invention, however, provides a jack capable of rapid height adjustment that differs from those jacks disclosed in the above-cited patents.
Another problem with the standard two-piece trailer jacks currently in use is the lack of sufficient jack capacity to raise the tongue of the trailer high enough off the ground to clear the knob on the hitch of a truck or other vehicle. For one reason or another, most of the jacks in use require 3-4 inches of blocks under the foot of the jack to provide enough height capacity to raise the trailer tongue to a height sufficient to attach the trailer to a truck. It would be desirable to have a jack with additional capacity to alleviate the need for using blocks.
The present invention provides an extendable jack with rapid advance and retraction that alleviates excessive cranking in the use of the jack. In addition, the present invention provides additional jack capacity of up to 20 inches or more over the standard trailer jack.